Intelligent input push rod assembly

ABSTRACT

An intelligent input push rod assembly for applying an input force from a brake pedal to a power booster of a brake system. The input push rod assembly includes a sensor that is capable of generating an electrical output having a magnitude that varies with the amount of force applied to the input push rod by the brake pedal. Preferably, the sensor generates an output voltage signal that is generally proportional to the input force applied to the input push rod. A shunt is provided so that springs associated with the sensor operate in a generally linear force-deflection range of the springs. The output signal generated by the sensor is applied to a brake light control system that is supported by the input push rod assembly. The brake light control system uses the signal generated by the sensor to determine whether the vehicle brake lights should be illuminated and also to cause direct illumination of the brake lights during a braking operation.

CROSS-REFERENCE

The present application is related to commonly owned U.S. Ser. No.09/941,036, filed on even date herewith, and U.S. Ser. No. 09/941,225,filed on even date herewith.

FIELD OF THE INVENTION

The present invention generally relates to power boosters for vehiclebrake systems and, more particularly, to an input push rod for applyingan input force from a brake pedal to the power booster.

BACKGROUND OF THE INVENTION

Brake power boosters generally utilize fluid pressure, or differentialsthereof, to provide a power assist in applying force to the mastercylinder of the brake system. Upon application of an input force on thebrake pedal, an input member such as a push rod activates the powerbooster. The power booster intensifies the force applied to the inputpush rod by a calibrated amount and transfers the force to a powerpiston which then moves the master cylinder to apply the brakes at eachwheel.

In the past, brake power boosters have incorporated electro-mechanicalswitches as part of the booster structure to cause illumination of thevehicle brake lights upon movement of the input rod. For example, powerboosters have been designed that include an electrical circuit coupledto the brake illumination control system that causes illumination of thebrake lights when the normally-open circuit is closed by a switch. Theswitch is typically biased in an open position and, in response totravel of the input push rod upon an input force being applied to thebrake pedal, moves to a closed position to complete an electricalcircuit that illuminates the brake lights. The brake illuminationcontrol circuit that includes a brake light driver circuit that causesillumination of the brake lights in response to closing of theelectro-mechanical switch. The brake light driver circuit is typicallyseparated or mounted remotely from the input push rod, and iselectrically coupled to the electro-mechanical switch through anelectrical cable.

Brake light control systems that use electro-mechanical switches tocause illumination of the vehicle brake lights have several drawbacks.For example, the brake booster and input push rod must be designed withadditional structures for housing the switch arrangement and forattaching the switch actuation components to the input push rod. Theseadditional structures increase the required space of the power boosterwhich can give rise to installation difficulties when space is limited.Mounting of the brake illumination control system remotely from theinput push rod and its associated electro-mechanical switch requiresadditional space and electrical connections within the vehicle.

Additionally, the electro-mechanical switch must be factory calibratedor adjusted to ensure that the brake lights are not illuminated when theinput push rod is in a rest position, but are properly illuminated inresponse to a predetermined limited travel of the input push rod upon aforce being applied to the brake pedal. Further, electro-mechanicalswitches used in brake light control systems may cause falseillumination of the brake lights when the switch is jostled or thedriver unintentionally causes travel of the input push rod in anon-braking situation.

For these general reasons, it would be desirable to provide a brakepower booster system that accurately and reliably illuminates brakelights of a vehicle in response to a driver's input on a brake pedalduring a braking situation.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing and other shortcomings anddrawbacks of brake systems heretofore known and, more particularly, ofbrake light control systems for causing illumination of brake lights.While the invention will be described in connection with certainembodiments, it will be understood that the invention is not limited tothese embodiments. On the contrary, the invention includes allalternatives, modifications and equivalents as may be included withinthe spirit and scope of the present invention.

In accordance with the principles of the present invention, anintelligent input push rod assembly is adapted to be operatively coupledat one end to a brake pedal and at an opposite end to a power booster ofa brake system. The input push rod assembly is capable of applying aforce to the power booster that is intensified and applied to a mastercylinder of the brake system through a power piston and force output rodto apply the brakes at each wheel.

In accordance with one aspect of the present invention, the input pushrod assembly includes a sensor that is capable of generating anelectrical output having a magnitude that varies with the amount offorce applied to the input push rod assembly by the brake pedal. Thesensor generates an output voltage signal having a magnitude that isgenerally proportional to the input force applied to the input push rodassembly by the brake pedal. The output voltage signal generated by thesensor is applied to a brake light illumination system that is supportedby the input push rod assembly. The brake light illumination system isoperable to directly illuminate the brake lights of vehicle in responseto the output voltage signal generated by the sensor. In this way, theinput push rod assembly is an integral assembly that imparts an inputforce to the power booster to initiate a braking operation and includesthe necessary brake light driver hardware to directly illuminate thebrake lights.

The input push rod assembly includes a pair of elongated input push rodmembers and a housing member operatively connecting the pair of inputpush rod members so that the input push rod members extend generallyalong a common axis. The input push rods are biased for movementrelative to each other by a spring and shunt assembly mounted within thehousing member. In one embodiment of the present invention, the springand shunt assembly comprises a pair of rigid shunt members thatcooperate with a pair of respective Belleville springs to bias the inputpush rods for movement relative to each other along the common axis inresponse to an input force applied to the input push rod assembly. Theshunt members are operable to limit compression or deflection of theBelleville springs through a generally linear force-deflection range ofthe springs so that the input push rods will move relative to each otheronly in the generally linear force-deflection operating range of theBelleville springs.

In accordance with another aspect of the present invention, the sensorcomprises a rare earth magnet and a linear Hall effect transducer thatare mounted generally within the housing member. The magnet is mountedor affixed to one of the input push rods, and the linear Hall effecttransducer is mounted or affixed to a printed circuit board mounted tothe housing member. The magnet and transducer are mounted offset fromthe common axis and in confronting relationship so that the magnet ismounted for reciprocal movement along a path parallel to and offset fromthe common axis, and the transducer is fixedly mounted adjacent the pathof reciprocal movement. In response to movement of the input push rodsrelative to each other, the sensor is operable to generate the outputvoltage signal having a magnitude that varies with the amount of forceapplied to the input push rod assembly by the brake pedal.

The brake light illumination system coupled to the sensor includes acontroller that executes an algorithm to perform two functions: (1) tocalibrate a brake pedal rest position or brake pedal rest force so thatthe sensor is automatically compensated for temperature variations,vehicle pedal assembly mechanical tolerance differences and brake pedalassembly component wear; and (2) to determine whether a sufficient brakeforce has been applied to the input push rod assembly to cause directillumination of the brake lights, thereby assuring that a predeterminedforce has been applied to the brake pedal before the brake lights areilluminated, and to turn the brake lights off at all other times.

The above features and advantages of the present invention will bebetter understood with reference to the accompanying figures anddetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the principles ofthe invention.

FIG. 1 is a side elevational view of an intelligent input push rodassembly in accordance with the principles of the present invention forapplying an input force to a power booster of a brake system and foractivating a vehicle's brake lights during a braking situation;

FIG. 2 is a partial cross-sectional view of the input push rod assemblytaken generally along line 2—2 of FIG. 1, and further illustrating theinput push rod assembly operatively connected to a power booster of abrake system;

FIG. 3 is an enlarged view of the encircled area 3 shown in FIG. 2,illustrating a force sensor in accordance with the principles of thepresent invention;

FIG. 4 is a cross-sectional view taken along line 4—4 of FIG. 2;

FIG. 5A is an enlarged view of the encircled area 5A shown in FIG. 2,illustrating a spring and shunt assembly in accordance with theprinciples of the present invention;

FIG. 5B is a view similar to FIG. 5A illustrating the spring and shuntassembly under an applied load;

FIG. 6 is a graph illustrating input force applied to the spring ofFIGS. 5A and 5B versus compression distance of the spring until thecompression is shunted;

FIG. 7 is a block diagram of a brake light illumination system inaccordance with the principles of the present invention;

FIG. 8 is a graph illustrating output voltage of the force sensor versusinput force applied to the input push rod assembly from a brake pedal inaccordance with the principles of the present invention;

FIG. 9 is a flow diagram illustrating process steps for calibrating abrake pedal rest position or brake pedal rest force in the brake lightillumination system of FIG. 7; and

FIG. 10 is a graph illustrating output voltage of the force sensorversus displacement in accordance with the principles of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the Figures, and to FIGS. 1 and 2 in particular, aninput push rod assembly 10 in accordance with the principles of thepresent invention is shown connected to a power booster 12 (FIG. 2) of abrake system, such as a power booster used in an automobile. Input pushrod assembly 10 has one end 14 adapted to be connected to a brake pedal(not shown) and another end 16 adapted to be connected to the powerbooster 12 so that input forces F_(I) applied to the input push rodassembly 10 through the brake pedal (not shown) will generateintensified output forces F_(O) to be applied to the master cylinder(not shown) of the brake system through force output rod 18 (FIG. 2) asis well known in the art. The power booster 12 intensifies the inputforce applied by the input push rod assembly 10 by a calibrated amountand transfers the force to a power piston 20 (FIG. 2) which then movesthe master cylinder (not shown) to apply the brakes at each wheel.

Power booster 12 may comprise a dual diaphragm vacuum operated boosterutilizing vacuum and atmospheric pressure differentials to boost inputforces F_(I) generating intensified output forces F_(O), however thepresent invention is also applicable to systems with a single diaphragmvacuum booster and with power boosters operating with other powersources without departing from the spirit and scope of the presentinvention. An exemplary dual diaphragm power booster for use with thepresent invention is fully disclosed in U.S. Pat. No. 6,006,649, ownedby the common assignee, and hereby expressly incorporated herein byreference in its entirety to which the reader is referred.

In accordance with the principles of the present invention, input pushrod assembly 10 includes a pair of elongated input push rod members 22and 24 that are operatively connected by a housing member 26 so that theinput push rod members 22 and 24 preferably extend substantially along acommon axis 28 (FIG. 2) and are effectively biased relative to eachother as will be described in detail below. As shown in FIG. 2, inputpush rod 22 includes an elongated cylindrical bore 30 near its rearwardend (i.e, the end facing away from the power booster 12) that slidablyreceives a forward cylindrical portion 32 of the input push rod 24 sothat the input push rods 22 and 24 are mounted for movement relative toeach other as described in detail below.

Further referring to FIG. 2, housing member 26 includes an elongatedstepped bore 34 that extends longitudinally therethrough. The steppedbore 34 includes a forward cylindrical bore 36 a formed near the forwardend of the housing member 26 (i.e, the end facing the power booster 12),an inner cylindrical bore 36 b, and a rearward cylindrical bore 36 cformed near the rearward end of the housing member 26 (i.e., the endfacing away from the power booster 12). The diameter of the stepped bore34 decreases from the rearward cylindrical bore 36 c having the largestdiameter to the forward cylindrical bore 36 a having the smallestdiameter. The inner cylindrical bore 36 b has a diameter intermediatethe diameters of the rearward and forward cylindrical bores 36 c and 36a, respectively.

As shown in FIG. 2, the forward cylindrical bore 36 a slidably receivesa rearward cylindrical portion 38 of the input push rod 22. As shown inFIGS. 2 and 4, a pin 40 extends transversely through the housing member26 in a transverse bore 42. The pin 40 is captured in an elongated slot44 (FIG. 2) formed in the input push rod 22 so that rotation of theinput push rod 22 about the common axis 28 is prevented, and the foreand aft travel or stroke of the input push rod 22 within the cylindricalbore 36 a of housing member 26 is limited by cooperation of the pin 40with fore and aft stops defined by the elongated slot 44 formed in theinput push rod 22.

The input push rod 24 is threadably connected to a nut 46 that isretained within the cylindrical bore 36 c between an annular shoulder 48of the stepped bore 34 and a retaining ring 50. In this way, the inputpush rod 24 is fixedly mounted to the housing member 26 for movementtherewith toward and way from the power booster 12 in response to forcesapplied to the input push rod assembly 10 by a brake pedal.

In accordance with one aspect of the present invention, the input pushrods 22 and 24 are biased for movement relative to each other by aspring and shunt assembly 52 mounted within the inner cylindrical bore36 b. The spring and shunt assembly 52 is mounted between an annularshoulder 54 of the stepped bore 34 and an annular disk 56 that issecured to the forward cylindrical portion 32 of the input push rod 24.In one embodiment of the present invention, as shown in FIGS. 5A and 5B,the spring and shunt assembly 52 comprises a pair of rigid shunt members58 that cooperate with a pair of respective Belleville springs 60 tobias the input push rods 22 and 24 for movement relative to each otheralong the common axis 28.

Each Belleville spring 60 has a larger diameter end 62 and a smallerdiameter end 64 that deflects toward the larger diameter end 62 duringcompression of the spring 60 under a load applied along a compressionaxis, such as along the common axis 28 in accordance with one embodimentof the present invention as shown. Each Belleville spring 60 has a freelength “l” (FIG. 5A) (i.e., a non-compressed length) and a fullycompressed length along the compression axis. Each of the shunt members58 includes a shunt body 66 that extends along the compression axis andhas an abutment surface 68 that is positioned intermediate the freelength and the fully compressed length of each respective spring 60 sothat the abutment surface 68 is positioned inwardly of the smallerdiameter end 64 of each spring 60 in an uncompressed state as shown inFIG. 5A.

In one embodiment, each shunt member 58 comprises a tubular sleeve 70that is mounted about the forward cylindrical portion 32 of the inputpush rod 24 and extends within the respective Belleville spring 60 sothat the spring 60 surrounds and is supported on the tubular sleeve 70.Each shunt member 58 has an annular flange 72 that extends radiallyoutwardly from the tubular sleeve 70 proximate one end thereof that isoperable to engage the larger diameter end 62 of the respectiveBelleville spring 60.

Further referring to FIGS. 2, 5A and 5B, the pair of shunt members 58are positioned to face each other so that the respective smallerdiameter ends 64 of the Belleville springs 60 engage each other to forma gap 74 (FIG. 5A) between the respective abutment surfaces 68 of theshunt bodies 66. In response to a force applied to the input push rodassembly 10 by a brake pedal, the housing member 26 and its connectedinput push rod 24 are translated forwardly toward the power booster 12.As this occurs, the housing member 26 and its connected input push rod24 move relative to the input push rod 22 as the spring and shuntassembly 52 is compressed between the rearward cylindrical portion 38 ofthe input push rod 22 and the annular disk 56 connected to the forwardcylindrical portion 32 of the input push rod 24, as shown in FIG. 5B.

During compression of the spring and shunt assembly 52, the gap 74formed between the respective abutment surfaces 68 of the shunt bodies66 closes until the abutment surfaces 68 engage each other as shown inFIG. 5B. Thereafter, continued application of an input force on theinput push rod assembly 10 is shunted through the shunt members 58 sothat the input force is transmitted to the input push rod 22 withoutfurther compression of the Belleville washers 60.

It will be appreciated by those of ordinary skill in the art thatBelleville springs 60 exhibit a generally linear force-deflectioncharacteristic over a limited deflection range of the spring, asillustrated in FIG. 6. For example, as shown in FIG. 6, the Bellevillesprings 60 exhibit a generally linear force-deflection characteristic upto a spring deflection distance “δ”. In accordance with the principlesof the present invention, each shunt member 58 is operable to limitcompression or deflection of the Belleville spring 60 to the deflectiondistance “δ” (see FIG. 5A) in response to a force applied to the inputpush rod assembly 10 by a brake pedal. Further deflection of theBelleville springs 60 beyond the deflection limit “δ” is shunted byshunt members 58, as indicated by the shaded area 76 in FIG. 6. In thisway, the input push rods 22 and 24 will move relative to each other onlyduring the generally linear force-deflection operation of the Bellevillesprings 60.

In accordance with another aspect of the present invention, a sensor 78,preferably in the form of a rare earth magnet 80 (FIG. 3) and a linearHall effect transducer 82 (FIG. 3), is mounted generally within thehousing member 26. In one embodiment of the present invention as shownin FIG. 2, the magnet 80 is mounted or affixed within a slot 84 formedin the rearward cylindrical portion 38 of the input push rod 22, and thelinear Hall effect transducer 82 is mounted or affixed to a printedcircuit board 86 (FIGS. 2 and 4) that is mounted within a cavity 88(FIGS. 2 and 4) of the housing member 26. As shown in FIGS. 2 and 4, themagnet 80 and transducer 82 are each mounted offset from the common axis28 and in confronting relationship so that the magnet 80 is mounted forreciprocal movement along a path 88 (FIG. 2) that is parallel to andoffset from the common axis 28, and the transducer 82 is fixedly mountedadjacent the path of reciprocal movement. An elongated slot 90 (FIG. 4)of sufficient width is formed in a wall 92 of the housing member 26 topermit electro-magnetic communication between the magnet 80 and thetransducer 82 during operation of the sensor 78.

Sensor 78 is operable to generate an electrical output that varies inmagnitude with the amount of force applied to the input push rodassembly 10 through the brake pedal (not shown), as illustrated by thegraph of FIG. 8 that shows the output voltage of the sensor 78 versusthe input force applied to input push rod assembly 10. As shown in FIG.8, the output voltage (V_(OUT)) of sensor 78 is generally proportionalto the input force applied to the input push rod assembly 10 over arange of input forces, such as between 0 and about 100 lbs., by way ofexample.

As the input force on the input push rod assembly 10 increases, themagnet 80 and the transducer 82 move relative to each other due to therelative movement of the input push rods 22 and 24 as described indetail above. As the length of the magnet 80 travels past the transducer82 in response to an input force applied to the input push rod assembly10, the output voltage of the transducer 82 increases as illustrated bythe graph of FIG. 10 that shows the output voltage of transducer 82versus the position of the magnet 80 relative to the transducer 82. Ofcourse, it will be appreciated that the orientation of the magnet 80 andtransducer 82 can be reversed, and the mounting of the magnet 80 andtransducer 82 relative to the common axis 28, can be changed withoutdeparting from the spirit and scope of the present invention. Whilemagnet 80 and linear Hall effect transducer 82 are shown and describedin connection with a preferred embodiment of the sensor 78, othersensors having electrical outputs that will vary in magnitude generallyproportionally with the amount of force applied to the input push rodassembly 10 are possible as well.

In accordance with yet another aspect of the present invention, as shownin FIGS. 2 and 7, the electrical output signal generated by thetransducer 82 is preferably applied to a brake light illumination system94 that is mounted on the printed circuit board 86 supported by thehousing member 26. As shown in FIG. 1, the brake light illuminationsystem 94 is coupled to brake lights 96, an anti-lock braking controlsystem (ABS) 98 and a vehicle stability control system 100 of a vehiclethrough electrical leads 102 extending from the housing member 26.

As will be described in detail below, the brake light illuminationsystem 94 is operable to directly illuminate the brake lights 96 of avehicle in response to an output signal generated by the transducer 82.As used herein, the term “directly illuminate” is used to describe thatthe brake illumination system 94, in accordance with one embodiment ofthe present invention, has the capability to activate the brake lights96 through an output signal applied to the brake lights 96 through theelectrical leads 102 without further processing of the output signalthrough a brake light driver circuit (not shown) mounted separately fromthe input push rod assembly 10. Additionally, the anti-lock brakingcontrol system (ABS) 98 and vehicle stability control system 100 mayreceive the output signal generated by the sensor 82, and use thisforce-related data for controlling other important vehicle functions aswell.

Referring to FIG. 7, the brake light illumination system 94 includes anA/D converter 104 (FIG. 7) that converts an analog voltage output signal106 generated by the transducer 78 into a digital signal 108. Thedigital signal 108 is applied as an input to a controller 110 of thebrake light illumination system 94 which includes logic described indetail below in connection with FIGS. 9 and 10 to determine whether asufficient brake force has been applied to the input push rod assembly10 to cause illumination of the brake lights 96. The magnitude of thedigital signal 108 applied to the controller 110 at which the brakelights 96 are illuminated may be chosen to correspond to an input forceon the input push rod assembly 10 that is indicative of an intendedbraking action by the driver. If a sufficient input force has beenapplied, the controller 110 generates an output signal 112 that isapplied to a brake light driver circuit 114 mounted on the printedcircuit board 86 that forms part of the brake light illumination system94.

The brake light driver circuit 114 includes a normally-open solid staterelay 116 that is coupled to the vehicle's electrical system 118. Inresponse to the output signal 112 generated by the controller 110, thebrake light driver circuit 114 closes the solid state relay 116 tocouple the vehicle's electrical system 118 to the brake lights 96 tothereby illuminate the brake lights 96 during a braking operation. Afterthe braking operation, the controller 110 applies an output signal 120to close the solid state relay 116 and thereby disconnect the vehicle'selectrical system 118 from the brake lights 56 to turn the brake lights56 off.

As shown in FIG. 9, the controller 110 executes an algorithm to performtwo functions: (1) to calibrate a brake pedal rest position or brakepedal rest force so that the sensor 78 is automatically compensated fortemperature variations, vehicle pedal assembly mechanical tolerancedifferences and brake pedal assembly component wear; and (2) todetermine whether a sufficient brake force has been applied to the inputpush rod assembly 10 to cause direct illumination of the brake lights96, thereby assuring that a predetermined force has been applied to thebrake pedal (not shown) before the brake lights 96 are illuminated, andto turn the brake lights 96 off at all other times.

Referring to FIGS. 9 and 10, at step 122, the controller 110 isinitially reset when the vehicle's key is turned to the “on” position.When the vehicle's key is turned to the “on” position, the controller110 initially stores or recalls at step 124 a previously determinedbrake rest force “F_(MIN)” value that represents a force on the brakepedal when it is at a rest position, i.e., the driver is not applyingany force to the brake pedal. The value “F_(MIN)” is determined by theoutput voltage of the sensor 78 that corresponds to the force applied tothe input push rod assembly 10 as described in detail above.

At step 126, the controller 110 determines whether the actual force“F_(ACT)” on the input push rod assembly 10, indicated by the outputvoltage of the sensor 78, is greater than or equal to the sum of thebrake pedal rest force “F_(MIN)” and a predetermined offset voltage“Δ_(ON)”. If so, the controller 110 causes illumination of the brakelights 96 at step 128 as described in detail above. Otherwise, at step130, the controller 110 determines whether the actual force “F_(ACT)” onthe input push rod assembly 10, indicated by the output voltage of thesensor 78, is less than or equal to the sum of the brake pedal restforce “F_(MIN)” and a predetermined offset voltage “Δ_(OFF)”. If so, thecontroller 110 causes the brake lights 96 to turn off at step 132 asdescribed in detail above.

If the actual force “F_(ACT)” on the input push rod assembly 10,indicated by the output voltage of the sensor 78, is not less than orequal to the sum of the brake pedal rest force “F_(MIN)” and thepredetermined offset voltage “Δ_(OFF)” as determined at step 130, thecontroller 110 next determines at step 134 whether the vehicle'sroadspeed is greater than or equal to a predetermined vehicle speedvalue, such as 2 MPH, thereby indicating that the vehicle is moving.

If the measured roadspeed is greater than or equal to the predeterminedroadspeed value as determined at step 134, the controller 110 nextdetermines at step 136 whether the vehicle is accelerating at anacceleration rate that is greater than or equal to a predeterminedacceleration value, thereby indicating that the driver is not applyingany input force to the input push rod assembly 10. If so, the controller110 stores the force on the brake pedal at step 124 as a new “F_(MIN)”value that represents a calibrated brake pedal rest force value for useby the algorithm executed by the controller 110. In this way, the sensor78 is automatically calibrated during operation of the vehicle tocompensate for temperature variations, vehicle pedal assembly mechanicaltolerance differences and brake pedal assembly component wear. As thoseof ordinary skill in the art will appreciate, the voltage output of thesensor 78 provides an indicia of the brake pedal rest position or,alternatively, the brake pedal rest force since both the brake pedalrest position and brake pedal rest force are related to the voltageoutput of the sensor 78.

The effect of the algorithm executed by controller 110 is illustrated inFIG. 10. If the actual force “F_(ACT)” on the input push rod assembly10, indicated by the output voltage of the sensor 78, is greater than orequal to the sum of the brake pedal rest force “F_(MIN)” and thepredetermined offset voltage “Δ_(ON)”, the controller 110 causesillumination of the brake lights 96. The brake lights 96 will remainilluminated until the actual force “F_(ACT)” on the input push rodassembly 10, indicated by the output voltage of the sensor 78, is lessthan or equal to the sum of the brake pedal rest force “F_(MIN)” and thepredetermined offset voltage “Δ_(OFF)”. Therefore, the state of thebrake lights 96 does not change if “F_(ACT)” is greater than the sum ofthe brake pedal rest force “F_(MIN)” and the predetermined offsetvoltage “Δ_(OFF)” and less than the sum of the brake pedal rest force“F_(MIN)” and the predetermined offset voltage “Δ_(ON)”. In this way,undesirable flickering of the brake lights 96 is avoided.

While the present invention has been illustrated by a description of apreferred embodiment and while this embodiment has been described insome detail, it is not the intention of the Applicants to restrict or inany way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. The various features of the invention may be usedalone or in numerous combinations depending on the needs and preferencesof the user. This has been a description of the present invention, alongwith the preferred methods of practicing the present invention ascurrently known.

However, the invention itself should only be defined by the appendedclaims, wherein we claim:
 1. Apparatus for providing a force to a powerbooster of a brake system, comprising: an input push rod assemblyincluding an elongated first input push rod member adapted to beoperatively coupled to a brake pedal and an elongated second input pushrod member mounted for movement relative to the first input push rodmember and adapted to be operatively coupled to a power booster of abrake system for providing a force to the power booster upon an inputforce being applied to the brake pedal; a sensor responsive to relativemovement between the first and second input push rod members and capableof generating an electrical output having a magnitude that varies withthe amount of input force applied to the input push rod by the brakepedal; and a brake light illumination system supported by the input pushrod assembly and coupled to the sensor, the brake light illuminationsystem being responsive to the electrical output generated by the sensorto directly illuminate brake lights of a vehicle.
 2. The apparatus ofclaim 1, wherein the input push rod assembly further comprises a housingmember operatively connecting the first and second input push rodmembers so that the first and second input push rod members extend alonga common axis.
 3. The apparatus of claim 2, wherein one of the first andsecond input push rod members is slidably received within the other ofthe first and second input push rod members for movement along thecommon axis.
 4. The apparatus of claim 2, wherein one of the first andsecond input push rod members is rigidly connected to the housing memberand the other of the first and second push rod members is slidablyreceived within the housing member for movement along the common axis.5. The apparatus of claim 2 further comprising a plurality of biasingelements mounted within the housing member and operable to apply abiasing force to effectively bias the first and second input push rodmembers for movement relative to each other along the common axis. 6.The apparatus of claim 5, wherein the biasing elements comprise aplurality of Belleville washers.
 7. The apparatus of claim 2, whereinthe sensor comprises a magnet and a Hall effect transducer.
 8. Theapparatus of claim 7, wherein at least one of the magnet and the Halleffect transducer is mounted offset from the common axis.
 9. Theapparatus of claim 8, wherein each of the magnet and the Hall effecttransducer is mounted offset from the common axis.
 10. The apparatus ofclaim 7, wherein one of the magnet and the Hall effect transducer ismounted for reciprocal movement along a path parallel to and offset fromthe common axis.
 11. The apparatus of claim 10, wherein the other of themagnet and the Hall effect transducer is fixedly mounted adjacent thepath of reciprocal movement.
 12. Apparatus for providing a force to apower booster of a brake system, comprising: a first input push rodmember having one end adapted to be operatively coupled to a brake pedaland an opposite free end; a second input push rod member having one endadapted to be operatively coupled to a power booster of a brake systemfor providing a force to the power booster upon an input force beingapplied to the brake pedal and an opposite free end; a housing memberoperatively supporting the free ends of the first and second input pushrod members so that the first and second push rod members extend along acommon axis; a plurality of biasing elements mounted within the housingmember and operable to bias the first and second input push rod membersfor movement relative to each other along the common axis in response toan input force applied to the brake pedal; and a sensor mounted offsetfrom the common axis and responsive to relative movement between thefirst and second input push rod members to generate an electrical outputhaving a magnitude that varies with the amount of input force applied tothe first input push rod by the brake pedal.
 13. The apparatus of claim12, further comprising a brake light illumination system supported bythe housing member and coupled to the sensor, the brake lightillumination system being responsive to the electrical output generatedby the sensor to directly illuminate brake lights of a vehicle.
 14. Theapparatus of claim 12, wherein one of the first and second input pushrod members is slidably received within the other of the first andsecond input push rod members for movement along the common axis. 15.The apparatus of claim 12, wherein one of the first and second inputpush rod members is rigidly connected to the housing member and theother of the first and second push rod members is slidably receivedwithin the housing member for movement along the common axis.
 16. Theapparatus of claim 12, wherein the biasing elements comprise a pluralityof Belleville washers.
 17. The apparatus of claim 12, wherein the sensorcomprises a magnet and a Hall effect transducer.
 18. The apparatus ofclaim 17, wherein at least one of the magnet and the Hall effecttransducer is mounted offset from the common axis.
 19. The apparatus ofclaim 18, wherein each of the magnet and the Hall effect transducer ismounted offset from the common axis.
 20. The apparatus of claim 17,wherein one of the magnet and the Hall effect transducer is mounted forreciprocal movement along a path parallel to and offset from the commonaxis.
 21. The apparatus of claim 20, wherein the other of the magnet andthe Hall effect transducer is fixedly mounted adjacent the path ofreciprocal movement.